It seems that the Personal Documents service will not accept KF8-only files, only hybrid files with both mobi and KF8 (or mobi only). And PDS has a 50MB limit. I have a few that are too big to send and was hoping to chop them in half as it were so I would not need to side-load them.

If mobiunpack could include a 'vestigial' mobi segment with the kf8 output, I have a feeling these would be accepted by PDS and one would still be able to realize the space savings of a kf8 only file. (though these would be unreadable on KDS K4iOS, etc.)

I hope to do some experimentation with media queries and kindlegen to confirm that this would make PDS happy.

[Update: turns out so far that I have been able to just kindlestrip these files to get them under 50MB (they included source file archive). It's more than okay that they remain hybrid when stored in PDS, since I might want to read with Kindle for iOS, which does not support KF8 reflowable yet. So I probably won't bother figuring out how to create a placeholder mobi.]